1. Field of the Invention
The invention relates generally to earth-boring drill bits used to drill a borehole for the ultimate recovery of oil, gas, or minerals. More particularly, the invention relates to improved, longer-lasting matrix and impregnated bit bodies. Still more particularly, the present invention relates to providing composite hard particle matrix materials with improved erosion resistance.
2. Background of the Invention
An earth-boring drill bit is typically mounted on the lower end of a drill string and is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. The borehole thus created will have a diameter generally equal to the diameter or “gage” of the drill bit.
The cost of drilling a borehole for recovery of hydrocarbons is very high, and is proportional to the length of time it takes to drill to the desired depth and location. The time required to drill the well, in turn, is affected by the number of times the drill bit must be changed before reaching the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipe, which may be miles long, must be retrieved from the borehole, section by section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which again must be constructed section by section. This process, known as a “trip” of the drill string, requires considerable time, effort and expense. Accordingly, it is desirable to employ drill bits which will drill faster and longer. The length of time that a drill bit may be employed before it must be changed depends upon a variety of factors, including the bit's rate of penetration (“ROP”), as well as its durability or ability to maintain a high or acceptable ROP. In turn, ROP and durability are dependent upon a number of factors, including the ability of the bit body to resist abrasion, erosion, and wear.
Bit performance is often limited by selective erosive damage to the bit body. Decreasing the erosive wear of bit bodies increases the footage per bit run and maintains the design intent of cutter exposure for optimal cutting, and hydraulic flow paths, and also reduces the propensity of lost cutters and junk in the hole.
Two predominant types of drill bits are roller cone bits and fixed cutter bits, also known as rotary drag bits. A common fixed cutter bit has a plurality of blades angularly spaced about the bit face. The blades generally project radially outward along the bit body and form flow channels there between. Further, cutter elements are typically mounted on the blades. The FC (fixed cutter) bit body may be formed from steel or from a composite material referred to as matrix.
To improve the erosion resistance of steel bit bodies, a protective hardfacing coating is often applied, where a harder or tougher material is applied to a base metal of the bit body. An example of a hardfacing is described in US 2010/0276208 A1; in which the maximum thickness of the hardphase of the protective coating is stated as limited to about 210 μm. Other thin coatings, typically less than about 0.500 μm, like HVOF (high velocity oxygen fuel) sprayed and electrolytic coatings with co-deposition of micron size hardphase, have also been used on FC steel bits to reduce erosive body wear. The effectiveness of a FC steel body bit in erosive applications is dependent on the coating integrity. Coating failure and exposure of the steel body can lead to accelerated erosive damage effecting bit performance and dull condition of bit.
The propensity of steel body bits to experience erosive damage when in service has been a primary reason for the use of FC matrix bits. Such matrix bit bodies typically are formed by integrally bonding or embedding a steel blank in a hard particulate (or hardphase) material volume, such as particles of WC (tungsten carbide), WC/W2C (cast carbide) or mixtures of both, and infiltrating the hardphase with a infiltrant binder (or infiltrant).
In fabricating such bit bodies, the cavity of a graphite mold is filled with a hardphase particulate material around a preformed steel blank positioned in the mold. The mold is then vibrated to increase the packing of the hardphase particles in the mold cavity. An infiltrant, such as a copper alloy is melted, and the hardphase particulate material is infiltrated with the molten alloy. The mold is cooled and solidifies the infiltrant, forming a composite matrix material, within which the steel blank is integrally bonded. The composite matrix bit body is removed from the mold and secured to a steel shank having a threaded end adapter to mate with the end of the drill string. PDC (Polycrystalline Diamond Compact) cutters are then bonded to the face of the bit in pockets that were cast.
PDC matrix bit bodies suffer from erosion during many drilling applications, and the damage to the blades and gage of such bits is often so extensive it cannot be repaired.
A conventional matrix body bit is typically comprised of hardphase particles of macrocrystalline WC or cast carbide of combinations thereof. The particle size distributions are typically optimized to provide high powder packing with tap densities of about 10.0 g/cc and hardphase particle size distributions typically range from 80 Mesh (177 μm) to 625 Mesh (20 μm). The maximum particle size used in a conventional hardphase is typically 180 μm with a typical average size of 50μ. The size of the particles make them prone to pullout in erosive applications, hence the matrix is prone to wear and erosive damage. A more erosion resistant material would therefore improve the dull condition of such bits, and allow longer runs, more runs per bit body, and improved repairability.
DuraShell™ is surface enhancement coating, developed to reduce erosion of matrix bits. The coating has a bi-modal hardphase distribution of large cast carbide particles of about 600 μm comprising about 65 wt % and 100 μm spherical cast carbide particles comprising about 35 wt %. A uniform distribution of hardphase constituents is produced by the use of a fugitive binder which typically comprises about 3 wt % of the hardphase mix. FIG. 1, depicts the position of erosion on a typical bit crown indicated by shaded areas, as such the mix is selectively applied to the corresponding areas on a mold surface (erosion resistant mix formulations can be applied to internal cavities within the bit, such as nozzle bores and to gage locations for erosion protection). The mold is then loaded with conventional hardphase powder and infiltrated with an alloy. The resultant bit body comprises selectively placed integral bonded surface enhancements, on the bit body where erosion is likely to occur.
FIG. 2 however, shows the microstructure of the integral bonded surface enhancement and exemplifies that the erosion resistance of the integral bonded surface enhancement is limited by preferential wear of the matrix binder due to its reduced hardness (typically about 125 VHN). The matrix therefore wears most quickly, exposing the hardphase particles leading to particle pull out and or cracking and fracturing of the surface. Therefore, there is a need to reduced the wear rate of the matrix and provide effective erosion resistance of such large particle surface enhancements.
Diamond shell surface enhancement coating, is another example of a surface enhancement developed with the aim of reducing erosion of matrix bits. The coating has a bi-modal hardphase distribution, comprising of about 15 wt % of 500 μm particles of diamond grit and about 85 wt % of macrocrystalline WC with an average particle size of about 50 μm. A uniform distribution of hardphase constituents is produced via the use of a fugitive binder which comprises about 3 wt % of the mix. The mix is selectively applied to areas of a mold surface where the bit body is prone to erosion. The mold is then loaded with a conventional hardphase powder and infiltrated with a Cu alloy. The resultant bit body comprises selectively placed diamond surface enhancements located on the bit body where erosion is likely to occur.
The diamond enhancement however, is limited by wear to the Cu alloy matrix binder (typical harness of 150 VHN) and subsequent pullout of the hardphase particles. Therefore it would be desirable to increase the hardness of the matrix, thereby reduce matrix wear rate and provide more effective erosion resistance of the large particle diamond surface enhancement.
The use of cemented carbide particles (for example WC-Co, WC-Ni, Metal-Carbide or combinations thereof) in composite matrix materials has typically been limited because when infiltrant interacts with the cemented carbide, a decrease in hardness of the resultant matrix is observed. The decrease in hardness is due in part to the increase in the mean free path of the hardphase after the cast body is cooled, and subsequent ease of pull out of the hardphase from the matrix.
The degradation of a commercially available matrix powder, (M2001 by Kennametal with MF53 copper alloy infiltrant) is shown in FIG. 3. The WC-Co cemented carbide particle had a pre-infiltration hardness of about 1300 VHN, which degraded to about 800 VHN on interaction with the infiltrant. FIG. 3, shows that the addition of a molten infiltrant to a dense hardphase of cemented hardphase particles results in a bloated hardphase within the matrix. The cemented hardphase particles post infiltration are typically 2 to 3 times larger in size than the cemented hardphase particles prior to infiltration.
Fixed-cutter bits comprised of infiltrated hardphase composites are further disclosed in U.S. Pat. Nos. 6,984,454, 3,149,411, 3,175,260, and 5,589,268. An example of a matrix composite using cemented carbide hardphase where degradation of the hard component was a concern is documented in U.S. Pat. No. 3,149,411. Infiltrant alloy chemistry was used to limit the degradation of the cemented carbide particles by using infiltrant alloys containing a metal from Group VIII, Series 4 of the Periodic Table (i.e., iron, cobalt or nickel) and minor amounts of chromium and boron.
Another example of a hardphase composite is documented in U.S. Pat. No. 3,175,260, where particles of cemented tungsten carbide or tungsten carbide alloy were heated and the molten matrix metal infiltrant poured into the mold containing the hard particles allowing the infiltrant to infiltrate the interstices of a mass of the hardphase. The melting point of the infiltrant ranged between about 1550° F. (843° C.) and 2400° F. (1316° C.) and decreasing the infiltration temperature and time was used as a method to suppress the interaction between the cemented carbide hardphase and the infiltrant during infiltration.
An example of selective placement of discrete inlays of hardphases with compositions that differ from the bulk material of the matrix body of a fixed cutter matrix bit are disclosed in U.S. Pat. No. 5,589,268 and U.S. Pat. No. 5,733,664. The art further discloses the fabrication of a composite comprising at least one discrete hardphase element held by a matrix powder wherein an infiltrant was infiltrated into the hard components.
One disclosed infiltrant was a copper-nickel-zinc alloy identified as MACROFIL 65, which has a melting point of about 1100° C. Another disclosed infiltrant was a copper-manganese-nickel-zinc-boron-silicon alloy identified as MACROFIL 53, having a melting point of about 1204° C. The art did not disclose a way to selectively use surface enhancements to increase erosion resistance.
U.S. Pat. No. 6,984,454 discloses a wear-resistant member that includes a hard composite member that is securely affixed to at least a portion of a support member. The hard composite is comprised of a plurality of hard components within a mold where an infiltrant alloy that has been infiltrated into the mass of the hard components.
The hard composite member disclosed in U.S. Pat. No. 6,984,454, consisted of multiple discrete hard constituents distributed in the composite member, the discrete hard constituents comprised one or more of: sintered cemented tungsten carbide, and a binder included one or more of cobalt, nickel, iron and molybdenum, coated sintered cemented tungsten carbide wherein a binder includes one or more of cobalt, nickel, iron and molybdenum, and the coating comprises one or more of nickel, cobalt, iron and molybdenum, and a matrix powder comprising hard particles wherein most of the hard particles of the matrix powder have a smaller size than the hard constituents. The infiltrant alloy employed had a melting point between about 500° C. to about 1400° C., and was infiltrated under heat into a mixture of the discrete hard constituents and the matrix powder so as to not effectively degrade the hard constituents upon infiltration. The hard constituents and the matrix powder and the infiltrant alloy were bonded together to form the hard composite member. However, degradation of the cemented carbide constituent was disclosed as an issue.
U.S. Pat. No. 6,045,750 discloses that a functional composite material for a steel bit roller cone body with erosion resistant wear surface enhancements can be achieved with high hardphase particle loading (high volume fraction), of about 75 volume %, and large constituent cemented carbide particle size by powder forging (solid state densification) cones The surface enhancement coating thickness in this case is limited in thickness to about three times the hardphase particle diameter and is constrained by the surface roughness or the texture of coating.
It is also known that powder-forged hard composite inlays, elements, or components with high cemented carbide loading and large constituent particles offer enhanced performance when used as cutting edges and wear surfaces in drill bits and other earth-engaging equipment. However, levels of achievable hard phase volume fractions are limited by geometric constraints on powder packing and by deformation/fracture behavior of particles during the forge cycle. In particular, coarse particle size fractions needed for maximizing packing density and wear resistance tend to bridge during forge densification, leading to voids and particle fracture defects in the densified composite. These problems are mitigated by formulation of powder preforms with at least one sintered cemented carbide particulate constituent of a composition, size, and residual porosity that imparts preferential plastic deformation and densification at forging temperature under local conditions of elevated pressure associated with particle contacts.
This functionality is provided by formulating a steel matrix of the hard composite using iron powder in the preform with a particle size less than 20 micrometers, in conjunction with the deformable partially porous sintered cemented carbide particulate constituent having a particle size that is between 5 to 100 micrometers. If the deformable sintered cemented carbide particulate constituent also has a nickel binder and another sintered cemented carbide hard phase constituent comprises a cobalt binder, useful strengthening of the matrix will be realized through the formation of tempered martensite halos around the cobalt binder carbide phase(s), due to nickel and cobalt diffusion and alloying of the surrounding iron matrix. The resulting hard composite microstructure exhibits increased resistance to the shear localization failure/wear progression [as disclosed in U.S. Pat. Appl. No. 2011/0031028 A1]. This publication, however is limited to steel body fixed cutter bit enhancements.
Hence, conventional FC composite materials that use large hardphase particle sizes to increase erosion resistance, often are limited by preferential matrix (binder) wear due to particle pullout and subsequent cracking and chipping damage to expose the primary large particles of the hard phase during service. Thus, a need exists for composite materials for use in bit body matrices and wear surfaces on drill bits and other earth-engaging equipment that provide surface enhancements with increased erosion resistance to improve bit performance in demanding downhole applications, thereby increasing bit footage/run, providing significantly better looking dulls, maintaining design intent of cutter exposure and hydraulic flow paths during the run and reducing risk of lost cutters in the hole.
As such, embodiments disclosed herein address the requirement for improved erosion resistance in composites used in bit body matrices and wear surfaces on drill bits and other earth-engaging equipment, as compared to certain conventional composites used and known in the art.